The present invention relates to radio frequency identification (RFID) tags. A tag serves to identify the thing to which it is attached. RFID tags can be attached to items to aid in their identification, speed checkout processing in a retail environment and aid in inventory management. The RFID tag is scanned or “interrogated” using radio frequency electromagnetic waves. Interrogating the RFID tag with radio waves allows the interrogator to be out of direct line-of-sight of the tagged item and located at a potentially greater distance from the item than is permitted with optical scanning.
RFID tags can be either active or passive. Active RFID tags carry their own energy source and passive tags derive their energy from the interrogator's radio signal. When a passive RFID tag is in the vicinity of an interrogator, its antenna receives energy from a radio signal broadcast by the interrogator. This energy is rectified and used to power the RFID tag's integrated circuit. After the passive tag's integrated circuit is powered on, it sends its information to the interrogator.
To reduce costs, inexpensive RFID tags generally do not have a conventional radio transmitter; instead, they communicate with a nearby interrogator using a communication technique known as “backscatter propagation.” Backscatter propagation involves modulating the antenna matching impedance of the RFID tag with the information to be sent to the interrogator. Modulating the impedance in this manner causes varying amounts of radio energy to be reflected from the tag's antenna, which are received and demodulated by the interrogator.
Backscatter propagation and other radio interrogation techniques allow an interrogator to identify a group of RFID tags en masse. While propagating radio waves over a wide area is advantageous to some RFID applications, it can be disadvantageous to other applications. Conventional RFID systems work well in typical checkout processing done at the point-of-sale because they detect the total items being purchased or checked out. Unfortunately, these RFID systems are not currently able to identify the actual position of individual items as the interrogators do not offer this level of granularity or functionality.
In a retail environment, groups of small items are often displayed on racks incorporating a number of item hangers. Lack of control over the grouping of items on display can also be disadvantageous. Item packages made for display on item hangers often have the same shape and appearance to ease stocking and arrangement of the item hangers. This can be confusing to customers who may select an item for inspection and inadvertently return it to a wrong location due to the similar appearances of nearby packages. For example, packages of camera film may appear identical at first glance, but closer inspection may reveal that the film speed is different or that one is for color prints and the other is for color slides. Manually searching for misplaced items and maintaining the order of items displayed on racks is time-consuming and expensive for retail operators.
Accordingly, there is a need for a system to identify groups of tagged items in a locality using RFID.
Like reference numbers and designations in the various drawings indicate like elements.